The present invention relates to an image data reconstructing device and an image display device and, more particularly, to transmission and reception of image data in an active matrix type liquid crystal display device.
With recent increases in screen size and resolution of display devices, necessity to reduce EMI generated by electronic apparatuses having display devices is increasing (e.g., MIKKEI MICRODEVICES, April 1997, p. 20, and NIKKEI ELECTRONICS, Nov. 3, 1997 (no. 702), pp. 123-148). xe2x80x9cLVDSxe2x80x9d, xe2x80x9cPanelLinkxe2x80x9d, xe2x80x9cSSCGxe2x80x9d, and some other methods (e.g., NIKKEI ELECTRONICS, Nov. 3, 1997 (no. 702), pp. 123-148) have been proposed as methods of reducing EMI generated by electronic apparatuses having display devices.
Although these methods can reduce EMI, they have such problems that relatively large additional circuits are necessary, and the driving frequency rises. In xe2x80x9cLVDSxe2x80x9d and xe2x80x9cPanelLinkxe2x80x9d, the voltage of, e.g., image data is lowered, and the driving frequency is raised.
This requires additional dedicated ICs (e.g., DS90CF561 and DS90CF562 (National Semiconductor)). It is difficult to incorporate a function of these dedicated ICs in a panel by using polysilicon TFTs (SID96 DIGEST pp. 21-24, and SID97 DIGEST pp. 45-48) or incorporate the functions of these dedicated ICs in the existing source driver IC (e.g., source driver IC in xe2x80x9cData Book, LCD TFT Drivers 1997 (TEXAS INSTRUMENTS)xe2x80x9d) or a gate array without largely changing the circuit configuration.
As described above, with the increases in size and resolution of liquid crystal display devices, necessity to reduce EMI generated by transmission of image data is increasing. However, the problems such as the large increase in circuit scale and the large change in circuit configuration must be solved to reduce EMI.
It is an object of the present invention to provide an image data reconstructing (decoding) device and an image display device capable of obtaining a satisfactory EMI reducing effect with addition of a small-scale circuit.
An image data reconstructing device according to the present invention is a device for receiving differential data of delayed previous image data and present image data from a data transmitting section and supplying a signal corresponding to the present image data reconstructed on the basis of the differential data to a display panel section having a plurality of pixels arranged in a matrix, comprising a holding circuit for holding image data reconstructed on the basis of the differential data received from the data transmitting section to delay the image data by a predetermined period, and an addition circuit for reconstructing the present image data by adding the previous image data obtained from the holding circuit to the differential data received from the data transmitting section.
In the present invention as described above, the differential data of the previous image data and the present image data is transmitted and received. The differential data is obtained by subtracting the previous image data from the present image data or vice versa. The previous image data is obtained by delaying image data by a predetermined period (e.g., about one to three pixel data periods, about one to three scanning line periods, about one to three field periods, or about one to three frame periods). The present image data and the previous image data often have a relationship as will be described later. Therefore, the number of transition times (the number of transition times from HIGH to LOW and vice versa) of the logic state of the differential data can be greatly reduced by appropriately choosing the delay period. By transmitting and receiving the differential data having this greatly reduced number of transmission times through a transmission line, EMI can be effectively reduced without largely increasing the circuit scale.
This image data reconstructing device can further comprise a delay period control circuit for changing delay period of the previous image data in accordance with a variation in a logic state of the differential data received from the data transmitting section.
The delay period for reducing the number of transition times of the differential data often varies in accordance with changes of images. Therefore, the delay period of the previous image data is properly changed such that the number of transition times of the differential data reduces. Consequently, the effect of reducing the number of transition times of the differential data can be obtained even when the image data changes.
In the image data reconstructing device, the holding circuit and the addition circuit are preferably integrated in a source driver IC for supplying a signal corresponding to the present image data reconstructed by the addition circuit to the pixel of the display panel section, and the holding circuit preferably serially supplies the previous image data to the addition circuit.
With this arrangement, the holding circuit and the addition circuit can be integrated in a source driver IC. Additionally, since the previous image data is serially supplied to the addition circuit, the addition circuit can be constructed by a few circuits.
In the image data reconstructing device, the image data reconstructing device preferably has a plurality of source drive ICs for supplying a signal corresponding to the present image data reconstructed by the addition circuit to the pixel of the display panel section, and the holding circuit and the addition circuit are integrated in each of the source driver ICs, and, dummy data is used, instead of the previous image data, when the previous image data to be supplied to the addition circuit integrated in one of the source driver IC is held by the holding circuit integrated in another source driver IC, to reconstruct the present image data by the addition circuit.
Since the present image data and the previous image data have a phase difference, a source driver IC for generating the present image data to be reconstructed is sometimes different from a source driver IC for holding the previous image data. If this is the case, external wirings to supply data need to be formed outside these source driver ICs. The use of the dummy data instead of the previous image data obviates the need for such external lines. So, the circuit area can be reduced as a whole.
In the image data reconstructing device, the holding circuit and the addition circuit can be integrated in a source driver IC for supplying a signal corresponding to the present image data reconstructed by the addition circuit to the pixel of the display panel section, and the source driver IC can hold at least one of the previous image data held by another source driver IC.
The present image data and the previous image data have a phase difference. Therefore, if a circuit for outputting the present image data to be reconstructed has the same number of bits as a circuit for holding the previous image data in the same source driver IC, the present image data cannot be reconstructed in some instances only by the same source driver IC. To reconstruct the image data by using data in another source driver IC, external wirings need to be formed outside these source driver ICs. If a source driver IC holds the previous image data held in another source driver IC, no such external lines are necessary. So, the circuit area can be reduced as a whole.
The image data reconstructing device can further comprise a supply circuit for supplying a signal corresponding to the present image data reconstructed by the addition circuit to the pixel of the display panel section, and a switching circuit for switching a driving capacity of the supply circuit in accordance with the differential data received from the data transmitting section.
By thus switching the driving capacity in accordance with the differential data, the static power consumption (particularly the static power consumption when the differential data is LOW) can be greatly reduced. As a consequence, the power consumption of the source driver IC can be reduced.
The image data reconstructing device can be constructed such that specific data is used instead of the previous image data in a specific period, and this specific data can be the same as data used instead of the previous image data in a specific period in the data transmitting section.
With this arrangement, even if an image data error occurs for some reason, normal operation can be restored within a short time by the use of the same data as the previous image data in both of the data transmitting section and the data receiving section (image data reconstructing device) in a specific period.
In the image data reconstructing device, the differential data received from the data transmitting section can be obtained by performing nonlinear conversion corresponding to generation frequency of each of original differential data for the original differential data, and the number of bits of the differential data is less than the number of bits of the original differential data, and the image data reconstructing device can further comprise a conversion circuit for performing nonlinear inverse conversion corresponding to the generation frequency of each of the original differential data for the differential data received from the data transmitting section, thereby increasing the number of bits of the received differential data.
As described above, the number of bits of the differential data can be reduced by performing nonlinear conversion/inverse conversion corresponding to the generation frequency of each of the differential data. Accordingly, the number of data transmission lines for transmitting the differential data can be reduced, so the ratio occupied by the data transmission lines in the whole apparatus can be reduced.
An image display device according to the present invention comprises a data transmitting section having a first holding circuit for holding image data to delay the image data by a predetermined period, and a sub tract ion circuit for generating differential data of previous image data obtained from the first holding circuit and present image data, a data receiving section having a second holding circuit for holding image data reconstructed on the basis of the differential data received from the data transmitting section to delay the image data by a predetermined period, and an addition circuit for reconstructing the present image data by adding the previous image data obtained from the second holding circuit to the differential data received from the data transmitting section, and a display panel section having a plurality of pixels arranged in a matrix, the display panel section receiving a signal corresponding to the present image data reconstructed by the addition circuit.
A liquid crystal display device according to the present invention comprises a data transmitting section having a first holding circuit for holding image data to delay the image data by a predetermined period, and a subtraction circuit for generating differential data of previous image data obtained from the first holding circuit and present image data, a data receiving section having a second holding circuit for holding image data reconstructed on the basis of the differential data received from the data transmitting section to delay the image data by a predetermined period, and an addition circuit for reconstructing the present image data by adding the previous image data obtained from the second holding circuit to the differential data received from the data transmitting section, and a liquid crystal display panel section having a plurality of pixels arranged in a matrix, transmittance of the pixel being controlled on the basis of a signal corresponding to the present image data reconstructed by the addition circuit.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.